MARINE EROSION
cliff
It can be
said that these are the most common and important erosional coastal landform,
due to their number and the amount of pressure human activity places upon them.
They result
from the interaction of a number of processes:
Geological.
Sub-aerial.
Marine.
Meteorological.
Human activity.
Cliffs are
steep if removal of material at its base is greater than supply.
Cliffs are
shallow if the supply of material is greater than removal.
A direct
relationship exists between rock type, erosion rate and cliff morphology.
Hard rock
cliffs:
Examples
include granite and basalt cliffs. They exhibit a slow rate of erosion and tend
to be stable.
Soft rock
cliffs:
Examples
include cliffs comprised of glacial till and clay, such as those found at
Fairlight Cove in Hastings.
These cliffs
often erode rapidly. In these cliffs, sub-aerial processes can contribute more
to erosion than marine processes, leading to mass movements such as sliding,
slumping and falls.
The diagram
below illustrates this:
Reasons for
cliff erosion at Holderness:
The cliffs
at Holderness have an average speed of retreat of 2m per year.
Cliffs are made of soft glacial till.
Till is easily eroded at base by waves,
resulting in instability.
Rainwater from above enters the till easily,
adding to its weight and instability.
Massive slumps and slides occur.
A similar
situation exists at Baton on sea in Hampshire and Beachy Head.
Headlands
and bays
Usually
found where less resistant and more resistant rock alternates. The less
resistant rock is attacked, first forming bays, and the stronger rock remains
as headlands. As wave refraction later occurs, energy becomes concentrated on
headlands, leaving them more liable to erosion.
Wave cut
platforms
These are
gently sloping features, often found extending from the base of a cliff. They
consist partly of material removed from the cliff (wave cut notch) as a result
of continual undercutting by waves. (See diagram below):
As
undercutting increases, the cliff slowly retreats, leaving a platform with an
angle of less than 4 degrees. The platform widens to a point, but due to the
cliff being attacked less frequently by waves, it is thought that they can only
reach a maximum of 0.5km.
Caves,
arches, stacks and blowholes
All of the
above are secondary features occurring during cliff formation. They originate
due to lines of weakness such as joints or faults being attacked and made
larger by marine erosion. Caves occur where the weakness is at the base of the
cliff, and can become a blowhole if the crack extends all the way to the
surface.
Caves formed
on either side of a headland may form an arch if the 2 caves join together.
Stacks are
collapsed arches.
Stumps are stacks that have been eroded and lost
height.
coppy right.
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